Outcomes and Safety of Single-Step and Multi-Step Antibiotic Drug Challenges
Saturday, March 5, 2016
South Exhibit Hall H (Convention Center)
Stephanie L. Mawhirt, DO, Luz S. Fonacier, MD FAAAAI, Rose Calixte, PhD, Mark A. Davis-Lorton, MD FAAAAI, Marcella R. Aquino, MD FAAAAI
Rationale:  Antibiotic challenge methods are varied in practice.  Compared to single-step challenges, multiple steps potentially offer increased safety.  We aimed to investigate the outcomes of single-step and multi-step challenges to determine dose-related challenge reactions.

Methods:  We conducted a five year retrospective study of patients with a history of antibiotic allergy undergoing antibiotic challenge.  Challenges were classified as 1-step (full-dose) or multi-step: 2-step (1/10th-remaining dose) and 3-step (1/100th-1/10th-remaining dose).  Gathered data included patient characteristics, index reaction history, and challenge outcome details.

Results: Antibiotic challenges were performed in 179 patients (mean age 62.6 years; 55.9% female).  Patients undergoing single or multi-step challenges had comparable demographics and index reaction severity.  Seventeen (9.5%) patients experienced challenge reactions: 5/48 penicillins, 3/76 cephalosporins, 6/48 carbapenems, and 3/7 fluoroquinolones.  Reactions occurred in [5/28] single-step and [12/151] multi-step challenges (17.9% vs. 7.9%).  A significant trend between a greater dose received and a positive challenge was observed as 70.6% of patients reacted on the full or remaining dose (p<0.001), however these reactions were less severe overall (rho=-0.53; 95% CI=-0.73 to -0.33).  Of 6 anaphylatic reactions (four 3-step, one 2-step, one full-dose), no reactions occurred on the 1/100th dose and the 2-step reacted on the 1/10th dose.

Conclusions:  Regardless of single or multi-step method utilization, the majority of patients reacted following the final dose administration and these reactions tended to be less severe.  Performing a 2-step challenge would have captured all anaphylactic reactions as no patients reacted on the first step of a 3-step challenge suggesting no conferred safety with 3-step challenges.